There are two main types of display panels: the matrix type and segment type. The matrix type is in widespread use because it can display any desired image. The segment type, on the other hand, is widely used in applications that display specific patterns, as in digital watches and mobile telephones.
A representative type of segment display panel is the seven-segment type which is used in such applications as pocket calculators. FIG. 1 shows an electrode layout in a seven-segment display panel 100. As shown in FIG. 1, seven segment electrodes 1 are arranged in a figure-eight pattern to display numbers, etc. To enhance the display capability, there is proposed a display panel having a background electrode 2 in an area surrounding the segment electrodes 1 (refer, for example, to patent document 1). By using the background electrode 2 in combination of the segment electrodes 1 for display, it is possible to present a reverse video display, etc., and the display capability can thus be enhanced.
The structure of the prior art segment display panel will be described below. FIGS. 2(a) to 2(c) are schematic diagrams showing the structure of one segment in the display panel 100 of FIG. 1. FIG. 2(a) is a plan view showing the segment electrode 1 and the background electrode 2 arranged around the periphery thereof. In the illustrated structure, the background electrode 2 is formed so as to surround the periphery of the segment electrode 1 by interposing a prescribed gap 3 therebetween. A segment lead wire 4 is provided which is electrically connected to the segment electrode 1 via a contact hole 5 to apply a voltage to the segment electrode 1. The gap refers to the spacing separating one electrode from the other in a direction parallel to the substrate.
FIG. 2(b) is a cross-sectional view taken along A-A in FIG. 2(a). The segment lead wire 4 formed from indium tin oxide (ITO) is provided on a first substrate 10 formed from a glass substrate, and an interlayer insulating film 11 is formed on the segment lead wire 4. The segment electrode 1 and the background electrode 2, both formed from ITO and separated from each other by the gap 3, are formed on the interlayer insulating film 11, and the segment electrode 1 and the segment lead wire 4 are electrically connected together through the contact hole 5. A second substrate 12 is disposed a prescribed distance apart from the first substrate 10, and a counter electrode 13 is formed on the second substrate 12. A liquid crystal 14 is sandwiched between the first substrate 10 and the second substrate 12. A desired display is produced by changing the orientation state of the liquid crystal 14 by applying a voltage between the segment electrode 1 and the counter electrode 13 or between the background electrode 2 and the counter electrode 13.
FIG. 2(c) is a cross-sectional view taken along B-B in FIG. 2(a). The cross section is identical in structure to that shown in FIG. 2(b), except that the segment lead wire is not provided on the first substrate 10 shown here. In the figure, the width of the gap 3 is denoted by d. Since the electrodes for driving the liquid crystal are not formed in the area where the gap 3 is formed, this area cannot be used to produce the display and, even if the segment electrode 1 and the background electrode 2 are driven at the same potential, the contour of the segment electrode becomes visible. It is therefore desirable to reduce the width d of the gap 3 to a visually imperceptible level.
Patent document 1: Japanese Unexamined Patent Publication No. H11-337960